The present invention relates to an apparatus for producing a toner, a method for producing a toner, and a toner.
As electrophotographic processes there are known many processes. An electrophotographic process normally includes a step of forming an electrostatic latent image on a photoreceptor by various means utilizing a photoelectrically-conductive material (exposing step), a development step of developing the latent image with a toner, a transfer step of transferring the toner onto a transferring material such as paper, and a step of fixing the toner image by heating, pressing or the like using a fixing roller.
Examples of the process for producing the toner for use in such an electrophotography include pulverizing process, polymerization process, and spray drying process.
In the pulverizing process, a starting material including a resin which is a main component (hereinafter simply referred to as “resin”) and a coloring agent is kneaded at a temperature of higher than the softening point of the resin to obtain a kneaded material which is then cooled and ground. The pulverizing process is advantageous in that the degree of selection of starting material is great, making it relatively easy to produce a desired toner. However, the toner obtained by pulverizing process has a great dispersion of shape among particles and a broad particle diameter distribution to disadvantage. As a result, the dispersion of chargeability, fixability, etc. among the toner particles is raised, thereby reducing the reliability of the toner as a whole.
In the polymerization process, a monomer which is a constituent of a resin is subjected to polymerization reaction in a liquid phase to produce a desired resin as a particulate toner. This polymerization process is advantageous in that the resulting particulate toner can be shaped in a form having a relatively high sphericity (close to geometrically complete sphere). However, the polymerization process cannot give a sufficiently small dispersion of particle diameter among the particles. This polymerization process normally involves the utilization of the interfacial properties of the polymerizable monomer with an aqueous medium in which it is dispersed to adjust the size of the particles thus obtained. However, in the case where such interfacial properties are utilized, it is normally essential that chemicals such as surface active agent be added to the aqueous medium. As a result, the toner thus obtained is affected by these chemicals and thus can be poor in electrical properties (chargeability) and environmental resistance such as moisture resistance. The polymerization process is also disadvantageous in that the degree of selection of resin material is small, making it difficult to obtain a toner having desired properties.
In the spray drying process, a high pressure gas is used to spray the starting material of toner dissolved in a solvent, thereby obtaining a finely divided powder as a toner. This spray drying process is advantageous in that the above pulverizing step is not required. However, this spray drying process involves the use of a high pressure gas to spray the starting material and thus can difficultly control the spray conditions of the starting material accurately. Therefore, it is made difficult to produce efficiently a particulate toner having a desired shape and size. Further, in the spray drying process, the dispersion of size of particles formed by spraying is great, raising the dispersion of moving rate of particles. Therefore, before the solidification of the starting material thus sprayed, the particles sprayed can be subject to collision and agglomeration to form an odd-shaped powder. Thus, the finally obtained particulate toner has an increased dispersion of shape and size. Accordingly, the toner obtained by spray drying process has a great dispersion of shape and size among the particles and hence a great dispersion of chargeability, fixability, etc. among the particles. As a result, the reliability of the toner is lowered as a whole.